Sensor and guide wire assemblies in which a sensor is mounted at the distal end of a guide wire are known. In U.S. Pat. Re. 35,648, which is assigned to the present assignee, an example of such a sensor and guide wire assembly is disclosed, where a sensor guide comprises a sensor element, an electronic unit, a signal transmitting cable connecting the sensor element to the electronic unit, a flexible tube having the cable and the sensor element disposed therein, a solid metal wire, and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, e.g. a membrane, with piezoresistive elements connected in a Wheatstone bridge-type of arrangement mounted thereon.
The above-mentioned solid metal wire, also called the core wire, extends from the distal end of the sensor guide to the proximal portion, where a male connector is arranged, and determines the overall mechanical properties, such as flexibility, torqueability and pushability, of the sensor guide. Sensor and guide wire assemblies for intravascular measurements are generally long, e.g. 100-300 cm, and have a small diameter, e.g. 0.35 mm. Thus, to provide the necessary stiffness and pushability, the solid metal wire must occupy a large portion of the available space inside the flexible tube, thereby leaving a very limited space for the sensitive signal transmitting conductors.
A different solution is suggested in a Japanese patent application, which is published under no. JP 2003-265617 and which discloses a sensor and guide wire assembly that has no core wire. The overall mechanical properties are instead provided by a hollow stranded wire, inside which electrical leads extend. Such a hollow stranded wire is, for example, sold by Asahi Intecc Co., Ltd. under the trademark Actone™. Besides a distal portion of the guide wire, where a pressure sensor is arranged inside a metallic casing, the hollow stranded wire extends along the length of the sensor guide. No flexible tube is therefore present in this sensor and guide wire assembly.
Although the latter way of constructing a sensor and guide wire assembly, with a hollow stranded wire and without a flexible proximal tube, could work in practise, the mechanical properties of the sensor guide can be improved.